1. Field of the Invention
The present invention relates to a method for forming an organic mask and a method for forming a pattern using the organic mask.
For the purpose of sufficiently explaining the current level of the art related to the present invention, descriptions of all patents, patent applications, patent gadgets, scientific literatures and the like quoted or specified herein are incorporated herein by reference in its entirety.
2. Description of the Related Art
A process for etching a base film using a resist pattern as a mask is an essential process for fabricating semiconductor devices. There are two types of etching, isotropic etching exemplified by wet etching and anisotropic etching exemplified by dry etching. The isotropic etching in the present invention means that the etching proceeds to right and left directions as well as up and down directions, while etching speeds of right and left directions are not always equal to those of up and down directions On the other hand, the anisotropic etching in the present invention means that etching speeds of right and left directions and up and down directions are substantially different such that the etching does not substantially proceed to under the organic mask. However, in the dry etching, the characteristics are different by, for example, a method of plasma discharge, a treatment pressure, an etching target material, and etching treatment gases, thereby resulting in rather isotropic (hereinafter, referred to as isotropic dry etching) in some case and rather anisotropic (hereinafter, referred to as anisotropic dry etching) in other case. A more suitable etching is selected from these etchings having different characteristics by considering practical etching conditions. When a side wall of the base film, which is etched using a resist pattern as a mask, is perpendicular or inverse tapered, if an upper film is formed after removing the resist mask, the step coverage becomes poor, thereby resulting in inducing film defects, for example, electrical insulation failure and breaking of wire. Therefore, an etched base film pattern is strongly requested to be tapered regardless of each etching methods described in the above.
A related art achieving a tapered angle of an etched base film using wet etching has been disclosed in reference 1 (Japanese Patent No. 3157634, paragraph No. 0013, 0014, FIG. 4). A resist is coated on a chromium film which is formed on a substrate as a base film to be etched. A resist pattern is formed through a light exposure process and a subsequent development process. For increasing hydrophilic property of the interface between the chromium film and the resist, a high hydrophilicity treatment is conducted under conditions of hydrophilicity saturation condition which is controlled by a liquid temperature and a dipping time of the treatment. The chromium film is wet etched and patterned to form a pattern having a taper. According to this related art, the etched edge of chromium film is tapered by implementing a hydrophilic treatment which increases hydrophilic property between the resist and the chromium film.
In addition, another related art taperizing a wet etched edge of chromium film, which is to be etched, has been disclosed in reference 2 (Japanese Laid-open Patent Publication No. 7-7757, fourth column 1-15 lines, FIG. 1). A resist which contains phenol novolac resin as a main chain is patterned into a predetermined pattern on a chromium film formed as a base film, which is to be etched, on a substrate. Then, the chromium film is wet etched with an etching solution containing nitric acid 2 mol/little or more, thereby resulting in a taper shape of the etched edge of chromium film. By dipping the substrate into the etching solution which is increased in concentration of nitric acid, the resist pattern is caused to peel off by the nitric acid of high concentration in the etching solution. In addition, the chromium film is oxidized by oxidants in the etching solution and released into the etching solution as ions. Accordingly, the etching proceeds. As a result, the etched edge of chromium film becomes a taper shape. That is, according to this related art, the etched edge of chromium film is tapered by increasing concentration of nitric acid in the etching solution.
A related art which taperizes a dry etched edge of chromium film, which is to be etched, has been disclosed in reference 3 (Japanese Laid-open Patent Publication No. 8-195505, paragraph No. 0019, 0020, FIG. 1). A p-n junction layer consisting of p-type GaP layer and n-type GaP layer is formed on GaP substrate. Then, a resist pattern is formed after coating a resist on the p-n junction layer through a light exposure process and a development process. After that, the resist pattern is distorted into a hemispheric shape using thermal reflow of the resist pattern. Through dry etching using the distorted resist pattern as a mask, the hemispheric shape pattern is copied on a film to be etched, while the resist recedes.
Another related art taperizing a dry etched edge of chromium film, which is to be etched, has been disclosed in reference 4 (Japanese Laid-open Patent Publication No. 2003-86493, paragraph No. 0011, FIG. 8). When a base material is dry etched using a normally tapered shape pattern as a mask, if an etching selectivity between the pattern and the base material is poor, the pattern thereof is reduced in the dry etching of the base material. Due to reduction of the pattern, a layer thickness at a skirt of the pattern gradually decreases in thickness, thereby partially decreasing in thickness of the base material pattern. However, defective shapes are caused at the edge of base material, thereby, failing in obtaining a desired length of the base material pattern.
The related arts disclosed in the four references which are described in the above are all able to achieve taperization of etching surface to be etched. However, the taper angle of the etched base film pattern is determined by the conditions of the resist mask and the etching thereof. Therefore it has been difficult to control and adjust the taper angle in wide range and with high accuracy.
In addition, in the related arts disclosed in references 1 and 2, when an adhesion strength of the resist mask with the base film before the treatment described in the references 1 and 2 is low, there has been a possibility that the taper angle may become too large compared with a desired angle, and the resist mask may be caused to peel off at a wet etching process which uses the resist mask. In addition, when the adhesion strength of the resist mask with the base is high, there has been a possibility that the taper angle may become too small, or not tapered in the technologies disclosed in the references 1 and 2.
Accordingly, it has been expected to provide a method for forming an organic mask and an etching method using the organic mask, which are free from the issues of the related arts.